Coupled instability of thin-walled members under combined bending moment, axial and shear force

In this paper we analyse the behaviour of thin-walled steel members with an I-shaped cross-section, in the presence of phenomena of coupled instability as overall-local type and combined state of stress of bending moment, axial and shear force. The analysis has been made by the ‘column model method’ and it has been used for bending moment-curvature-axial force diagrams, modified by the presence of local instability for web buckling of steel beams.

The previous analysis allows one to define interaction diagrams M_Imax−λ−N, which can be used to check the steel members in relation to the overall slenderness and the local slenderness of the web panel.     

Free vibration of shear beams with finite rotational inertia

Free vibration of shear beams is studied when rotational motion is taken into account, while classical shear beams do not consider rotational motion. From a single governing equation of Timoshenko beams, we analytically derive Rayleigh beams and shear beams as two limiting cases of the ratio of reduced shear stiffness to bending stiffness being sufficiently large and small, respectively. Emphasis is placed on the analysis of free vibration of nonclassical shear beams without damping effect. Under the condition of general end restraints, a characteristic equation for nonclassical shear beams with finite rotational inertia is derived in explicit form. A condition that the nonclassical shear beams reduce to the classical ones is found, and classical shear beams may be understood as nonclassical ones with infinite large rotational inertia. Nonclassical natural frequencies and mode shapes are calculated for a standing shear beam on an elastic foundation. Previous results of pinned-free, and free-free shear beams can be taken as special cases of the present analysis. The effects of finite rotational inertia, material properties, geometrical conditions and end restraints on the natural frequencies of shear beams are discussed.     

考虑剪力滞效应的简支箱梁自振特性

由于箱梁中剪力滞效应的存在,通常采用的一般梁理论计算简支箱梁的振动频率会产生较大的误差,对于宽跨比较大的简支箱梁振动计算误差尤其明显.在考虑了箱梁剪力滞效应的基础上,利用能量变分原理分析了简支箱梁的自由振动,得到了考虑剪力滞效应的简支箱梁自振基频的解析解.算例表明该法比一般梁理论计算精度有显著提高,且计算简单方便.最后,考虑剪力滞效应对箱形梁结构自振特性的影响进行了讨论,发现考虑剪力滞效应后简支箱梁的振动基频降低,且箱梁的宽跨比对其降低程度影响最为显著.     

部分埋入弹性地基的变截面桩自由振动(英文)

阐述了部分埋入弹性地基的变截面桩的自振频率和振型的数值计算方法,并推导了桩顶作用轴向荷载的变截面桩的控制自由振动的微分方程,最后把此微分方程应用于 Ｒｕｎｇｅ － Ｋｕｔｔａ 法和 Ｒｅｇｕｌａ － Ｆａｌｓｉ 法,采用特征值搜索法算出桩的自振频率和振型。     

轴力和弯矩共同作用下盾构隧道纵向非线性等效抗弯刚度研究

实际工程中,盾构隧道纵向弯矩和轴力可能同时存在,若按传统的纯弯等效抗弯刚度计算可能会带来较大误差。考虑轴力和弯矩共同作用对纵向弯曲变形的影响,提出5种弯曲模式,在经典的志波模型的基础上,建立盾构隧道纵向等效抗弯刚度计算模型,基于该模型开发了计算程序,以成都地铁3号线盾构隧道为实例,对其纵向等效抗弯刚度和管环张开量随轴力和弯矩的发展规律进行分析,并讨论弯曲模式的实用判别方法,求出变形过程的临界弯矩,最后给出纵向弯曲变形为线性和非线性的内力条件。研究发现:盾构隧道纵向变形随弯矩的发展过程可按轴力分为4类,各过程下管环张开量和等效抗弯刚度随弯矩的发展规律十分不同;轴力对等效抗弯刚度有显著影响,一般呈现压弯纯弯拉弯的规律。研究成果可应用于盾构隧道结构纵向力学分析、抗弯刚度分析等方面。     

干振碎石桩处理新近填土效果检测

结合一大型厂房工程实例，以效果检测数据库依据，就干振碎石桩加固处理填土进行了效果检测分析与评价，指出干振碎石桩处理浅层软弱地基土技术可靠，成本低，工期短的优点。     

Free vibration analysis of functionally graded cylindrical shells including thermal effects

Free vibration analysis of simply supported FG cylindrical shells for four sets of in-plane boundary conditions is performed. The material properties are assumed to be temperature-dependant and gradually changed in the thickness direction of the shell. The effects of temperature rise are investigated by specifying arbitrary high temperature on the outer surface and the ambient temperature on the inner surface of the cylinder. Distribution of temperature across the shell thickness is found from steady state heat conduction only in the thickness direction. The equations of motion are based on Love's shell theory and the von Karman–Donnell-type of kinematic nonlinearity. The static analysis is first performed to determine the prestressed state induced by the thermal loadings, using the exact solution of the governing equations and then the equations of motion are solved by Galerkin's method. The results are obtained to indicate the effects of power law index on the natural frequencies and corresponding mode shapes in the thermal environment.     

A new approach for free vibration analysis of nonuniform tall building structures with axial force effects

Dynamic analysis of beam‐like structures is significantly important in modeling actual cases such as tall buildings and several other related applications as well. This article studies free vibration analysis of tall buildings with nonuniform cross‐section structures. A novel and simple approach is presented to solve natural frequencies of free vibration of cantilevered tall structures with variable flexural rigidity and mass densities. These systems could be replaced by a cantilever Timoshenko beam with varying cross‐sections. The governing partial differential equation for vibration of a nonuniform Timoshenko beam under variable axial loads is transformed with varying coefficients to its weak form of integral equations. Natural frequencies can be determined by requiring the resulting integral equation, which has a nontrivial solution. The presented method in this study has fast convergence. Including high accuracy for the obtained numerical results as well. Numerical examples including framed tube as well as tube‐in‐tube structures are carried out in the study and compared with available results in the literature, and also with the results obtained from finite element analysis in order to show the accuracy of the proposed method in the study. Obtained results indicate that the presented method in this study is powerful enough for the free vibration analysis of tall buildings.     

基于Novak薄层法的部分埋入式单桩的扭转振动

在Novak平面假定的基础上将土体视为由无穷多带一圆孔的薄的土层组成,求得等效Winkler扭转弹簧-阻尼器的刚度系数和阻尼系数,在此基础上建立了部分埋入式单桩埋入部分和外露部分桩基的扭转振动微分方程,利用部分埋入式单桩的连续条件和边界条件求解了部分埋入式单桩的扭转振动。部分埋入式单桩的扭转振动与完全埋入式单桩一样都存在有共振现象,当外露部分桩长减小时部分埋入式单桩的扭转振动可以退化到完全埋入式单桩的情况,土体剪切模量越大,土体对桩基的扭转作用越大。     

Free vibration of quadrilateral laminated plates with carbon nanotube reinforced composite layers

The free vibration behavior of quadrilateral laminated thin-to-moderately thick plates with carbon nanotube reinforced composite (CNTRC) layers is studied. The governing equations are based on the first-order shear deformation theory (FSDT). The solution procedure is based on transforming the governing differential equations from an arbitrary straight-sided physical domain to a regular computational one, and discretization of the spatial derivatives by employing the differential quadrature method (DQM) as an efficient and accurate numerical tool. Four different profiles of single walled carbon nanotubes (SWCNTs) distribution through the thickness of layers are considered, which are uniformly distributed (UD) and three others are functionally graded (FG) distributions. The fast rate of convergence of the presented approach is numerically demonstrated and to show its high accuracy, wherever possible comparison studies with the available results in the open literature are performed. Then, the effects of volume fraction of carbon nanotubes (CNTs), geometrical shape parameters, thickness-to-length and aspect ratios, different kinds of CNTs distribution along the layers thickness and different boundary conditions on the natural frequencies of laminated plates are studied.     

Free vibration of non-uniformly ring stiffened cylindrical shells using analytical, experimental and numerical methods

In this research, the free vibration analysis of cylindrical shells with circumferential stiffeners, i.e. rings with non-uniform stiffeners eccentricity and unequal stiffeners spacing is investigated using analytical, experimental and finite elements (FE) methods. Ritz method is applied in analytical solution while stiffeners treated as discrete elements. The polynomial functions are used for Ritz functions and natural frequency results for simply supported stiffened cylindrical shell with equal rings spacing and constant eccentricity is compared with other's analytical and experimental results, which showed good agreement. Also, a stiffened shell with unequal rings spacing and non-uniform eccentricity with free–free boundary condition is considered using analytical, experimental and FE methods. In experimental method, modal testing is performed to obtain modal parameters, including natural frequencies, mode shapes and damping in each mode. In FE method, two types of modeling, including shell and beam elements and solid element are used, applying ANSYS software. The analytical and the FE results are compared with the experimental one, showing good agreements. Because of insufficient experimental modal data for non-uniformly stiffeners distribution, the results of modal testing obtained in this study could be as useful reference for validating the accuracy of other analytical and numerical methods for free vibration analysis.     

Finite element analysis of CFT columns subjected to an axial compressive force and bending moment in combination

Proper material constitutive models for concrete-filled tube (CFT) columns subjected to an axial compressive force and bending moment in combination are proposed and verified in this paper by using the nonlinear finite element program ABAQUS compared against experimental data. In the numerical analysis, the cross sections of the CFT columns are categorized into three groups, i.e., ones with circular sections, ones with square sections, and ones with square sections stiffened with reinforcing ties.It is shown that the steel tubes can provide a good confining effect on the concrete core when the axial compressive force is large. The confining effect of a square CFT stiffened by reinforcing ties is stronger than that of the same square CFT without stiffening ties but weaker than that of a circular CFT. Nevertheless, when the spacing of reinforcing ties is small, a CFT with a square section might possibly achieve the same confining effect as one with a circular section.     

Free vibration of composite plates using the finite difference method

The finite difference method was used to solve differential equations of motion of free vibration of composite plates with different boundary conditions. The effects of shear deformation and rotary inertia on the natural frequencies of laminated composite plates are investigated in this paper. Four cases are studied: neglecting both shear deformation and rotary inertia, considering only rotary inertia, considering only shear deformation, and considering both. Solutions were obtained for symmetric and angle-ply laminated plates. The factors that affect natural frequencies of different composite plates, such as span-to-depth ratio, aspect ratio, angle-ply, and lamination sequence were also investigated. Results were found to agree well with exact and approximate solutions reported in literature. Shear deformation showed a considerable effect on the natural frequencies for composite plates, whereas the rotary inertia effect was found to be negligible.     

带减振架的吊索索力测试研究

对索力测试频率法进行了研究，采用集中荷载作用下的长索受迫振动模型模拟了带减振架的吊索振动问题，利用Laplace变换推导出带减振架的吊索索力和基频直接的关系，并应用于工程实际，具有较高的推广价值。     

纵向振动桩侧壁切应力频率域解及其应用

利用Fourier变换 ,得到纵向振动桩在简化条件下侧壁切应力的频率域表达式 ,应用该表达式获得桩周土的等效刚度系数k和等效阻尼系数c的计算式 ,它们是桩周土剪切波速和密度、桩半径和振动频率的函数 ,把它们用于桩瞬态纵向振动计算 ,并与工程桩反射波法动测曲线进行对比 ,两者有较好的一致性     

Free vibration analysis of circular thin plates with stepped thickness by the DSC element method

Novel formulation is presented by using the discrete singular convolution (DSC) for free vibration analysis of circular thin plates with uniform and stepped thickness. Different from the commonly used ones in literature, regularity conditions are not needed at the circular plate center point to avoid singularity. DSC circular and annular thin plate elements are established. For the DSC circular plate element with radius of R₁, the stiffness equation is first formulated in region [−R₁, R₁] with even number of nodes and then reduced to region [0, R₁] by using either symmetric or anti-symmetric conditions. The proposed DSC circular and annular plate elements are used for obtaining frequencies of uniform/stepped circular thin plates or annular thin plates with different boundary conditions. Comparison of the present DSC results to existing analytic and numerical solutions verifies the proposed formulations. The present research extends the DSC method to free vibration of circular thin plates with stepped thicknesses.     

截面轴力与弯矩屈服面在钢框架动力弹塑性分析中的应用

为了在现行规范下考虑轴力与弯矩的相互作用,并兼顾计算精度与计算效率,研究了截面屈服面在钢框架动力弹塑性分析中的新应用。首先选用截面组合思想构建轴力与弯矩的屈服面。接着,基于经典塑性理论建立截面恢复力模型,并给出了截面状态确定方法。然后阐述了基于力的梁柱单元状态确定过程及其对截面恢复力模型的调用。最后采用alpha-OS积分算法,对一个四层两跨钢框架开展了动力弹塑性分析。结果表明：截面轴力弯矩屈服面能很好地考虑轴力存在及变化对截面弯矩承载力的影响,基于屈服面的恢复力模型在计算精度上远高于塑性铰模型并逼近纤维模型,在效率上远高于纤维模型,可以用于钢框架的动力结构弹塑性分析。     

木梁柱螺栓钢填板节点转动性能理论计算方法

文章首先通过单调加载试验研究胶合木梁柱螺栓钢填板节点在弯剪复合作用下的转动性能,随后基于Johanson屈服模型提出胶合木梁柱钢填板螺栓节点在弯剪复合作用下的极限承载力和节点刚度的计算方法;同时提出节点弯矩转角曲线的理论预测模型.理论计算与试验结果相比具有较高的准确性.最后,基于节点承载力的理论计算方法分析节点抗剪承载...     

双排抗滑桩在边坡中受力分析与计算的探讨

对边坡中双排抗滑桩的受力进行了总结,同时分析了桩布置和排距对双排桩内力的影响,根据其受力特点,归纳了双排桩的计算模式和布置方式,并根据具体实例探讨了计算模式的可行性。     

Nonlinear free vibration of skew nanoplates with surface and small scale effects

The nonlinear free flexural vibration of skew nanoplates is studied by considering the influences of free surface energy and size effect (small scale) simultaneously. The formulations are derived based on classical plate theory (CPT) in conjunction with nonlocal and surface elasticity theories using Hamilton's principle. Green's strain tensor together with von Kármán assumptions is employed to model the geometrical nonlinearity. The free surfaces are modeled as two-dimensional membranes adhering to the underlying bulk material without slipping. The solution algorithm is based on the transformation of the governing differential equation from the physical domain to a rectangular computational one, and discretization of the spatial derivatives by employing the differential quadrature method (DQM) as an efficient and accurate numerical tool. The effect of small scale parameter and surface effect together with the geometrical parameters and boundary conditions on the nonlinear frequency parameters of the skew nanoplates are studied.